Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A surgeon introduces a catheter assembly having a balloon portion percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The surgeon advances the catheter assembly through the coronary vasculature until the balloon portion crosses the occlusive lesion. Once in position, the surgeon inflates the balloon to radially compress the atherosclerotic plaque of the lesion and remodel the vessel wall. The surgeon then deflates the balloon to remove the catheter.
But this procedure can create intimal flaps or tear arterial linings, which can collapse and occlude the vessel after balloon removal. Moreover, thrombosis and restenosis of the artery may develop over several months following the procedure, which may require another angioplasty procedure or a by-pass operation. To reduce artery occlusion, thrombosis, and restenosis, the surgeon can implant a stent into the vessel.
Stents are used not only mechanically, but also to provide biological therapy. Mechanically, stents act as scaffoldings, physically holding open and, if desired, expanding the vessel wall. Typically, stents compress for insertion through small vessels and then expand to a larger diameter once in position. U.S. Pat. No. 4,733,665, issued to Palmaz; U.S. Pat. No. 4,800,882, issued to Gianturco; and U.S. Pat. No. 4,886,062, issued to Wiktor disclose examples of PTCA stents.
Medicating the stent provides for pharmacological therapy. Medicated stents allow local drug administration at the diseased site. To provide an effective drug concentration at the treated site, systemic treatment often requires concentrations that produce adverse or toxic effects. Local delivery advantageously allows for smaller systemic drug levels in comparison to systemic treatment. Because of this, local delivery produces fewer side effects and achieves more favorable results. One proposed method for medicating stents involves coating a polymeric carrier onto a stent surface. This method applies a solution that includes a solvent, a dissolved polymer, and a dissolved or dispersed drug to the stent. As the solvent evaporates, it leaves a drug impregnated, polymer coating on the stent.
Current biomaterials research aims at controlling protein adsorption on implantable medical devices. Current biomaterials exhibit uncontrolled protein adsorption, leading to a mixed layer of partially denatured proteins. Current surfaces contain different cell binding sites resulting from adsorbed proteins such as fibrinogen and immunoglobulin G. Platelets and inflammatory cells such as macrophages and neutrophils adhere to these surfaces. When so activated, these cells secret a wide variety of pro-inflammatory and proliferative factors. Non-fouling surfaces control these events. Thus surfaces absorb little or no protein, primarily due to their hydrophilicity. One prior art approach creates these surfaces by using hyaluronic acid and polyethylene glycol. Non-fouling surfaces or coatings are a subset of biobeneficial coatings. Biobeneficial coatings benefit the treatment site without releasing pharmaceutically or therapeutically active agents, (“drug(s)”). Another type of biobeneficial coating contains free-radical scavengers, which preserve nitric oxide and prevent oxidative damage.